The long term goal of the proposed research is to gain an understanding of influenza virus structural components (genes and proteins), their antigenic domains, their interaction with antibody, and their role in stimulating long lasting protective immunity. This information is vital to the development of vaccines and antiviral agents. Utilizing knowledge gained during the current grant period on the three-dimensional (3D) structure of an influenza virus neuraminidase antibody complex and with the available structural information in the uncomplexed hemagglutinin and neuraminidase we propose the following aims to reach our long term goal. 1) Elucidation of the mechanism of inhibition of the functional domains on the NA and HA of influenza virus with antibodies and inhibitors. 2) Elucidation of molecular basis of virulence of influenza viruses. 3) Determination of the optimal combination of influenza gene products for induction of protective immunity. The 3D structure of antibody complexed with either NA or HA will be established by X-ray crystallographic analysis and correlated with the ability of the antibodies to protect against infection with highly virulent influenza viruses. The HA of a mammalian influenza virus possessing multiple basic amino acids in its connecting peptide will be evaluated for its ability to contribute virulence to reassortant viruses containing various gene constellation. Each of the cloned genes of the highly virulent chicken H5N2 influenza virus will be expressed in several vector systems and their ability to induce protection or potentiate infection in mice and chickens will be determined. There is accumulating evidence that genes from influenza virus that have affected humans in the past are probably maintained in the gene pool in nature and there is a history of reappearance of human influenza viruses (e.g., H1N1). Thus, the potential for the reappearance of a highly virulent virus (vis-a-vis the 1918 "Spanish" influenza) remains a distinct possibility that our research is directed against.